The present invention relates to hydrocarbon soluble or dispersible cyclic phosphates, their method of preparation and their utility as an additive for oleaginous compositions including, fuel oil, lubricating oils, including greases, industrial oils, gear oils, power transmitting fluids, and engine lubricating oils.
There are many instances, as is well known, particularly under boundary lubrication conditions where two moving surfaces in contact with each other must be lubricated, or otherwise protected, so as to prevent wear, and to insure continued movement. There are other instances where friction between two rubbing surfaces is sought to be modified but not necessarily minimized. By controlling friction between two surfaces, the power required to impart movement from one surface to another is also controlled.
For example, a specialized property sought to be imparted to certain lube oil compositions adapted for use as an automatic transmission fluid is the friction modification characteristic of the fluid. This property distinguishes automatic transmission fluids (ATF) from other lubricants, and in fact between types of ATF as well. Such characteristic quality has received the most attention by both the transmission manufacturers and fluid producers for many years. This attention stems from the fact that the friction requirements of an ATF are unique and depend on the transmission and clutch design, as well as on the type of clutch plate material used.
Another property sought to be imparted to lubricating oil compositions including automatic transmission fluids is reduced wear such as bearing and power component wear.
As is also well known, both wear and friction modification can be controlled through the addition of suitable additives with varying degrees of success.
While there are many known additives which may be classified as antiwear, or friction modifying agents, it is also known that many of these additives act in a different physical or chemical manner and often compete with one another, e.g. they may compete for the surface of the moving metal parts which are subjected to lubrication. Accordingly, extreme care must be exercised in the selection of these additives to insure compatibility and effectiveness.
The metal dihydrocarbyl dithiophosphates are one of the additives which are known to exhibit antioxidant and antiwear properties. The most commonly used additives of this class are the zinc dialkyl dithiophosphates (ZDDP) which are conventionally used in lubricant compositions. While such zinc compounds afford excellent oxidation resistances and exhibit superior anti-wear properties, it has heretofore been believed that the same significantly limits the ability to control the friction modification properties of the fluid.
Both anti-wear and friction modifying agents function by forming a coating on the surface of the moving metal parts. The coating bonds are generally effected physically and/or chemically. Consequently, if the bonding between the anti-wear agent and the metal part is stronger than the bonding between the friction modifying agent and the metal part, the anti-wear agent will displace the friction modifying agent at metal surface, i.e. at the metal/fluid lubrication boundary interface. This results in a loss in the ability of the friction modifying agent to exert its intended effect.
Unfortunately, while ZDDP is recognized as an industry wide standard for imparting anti-wear properties to lubricating compositions, it has been found that it also exhibits a greater affinity for the metal surface than available friction modifying agents.
Various tests have been designed by auto manufacturers for measuring ATF friction and anti-wear properties which if passed are indicative of the fact that such properties will match the requirements of particular transmission designs and result in transmission durability and smooth shifting under a variety of road conditions.
Friction modification is typically evaluated on an SAE No. 2 friction apparatus. In this test, the motor and flywheel of the friction machine (filled with fluid to be tested) are accelerated to constant speed, the motor is shut off and the flywheel speed is decreased to zero by application of the clutch. The clutch plates are then released, the flywheel is again accelerated to constant speed, and the clutch pack which is immersed in the test fluid is engaged again. This process is repeated many times with each clutch engagement being called a cycle.
During the clutch application, friction torque is recorded as a function of time. The friction data obtained are either the torque traces themselves or friction coefficients calculated from the torque traces. The shape of the torque trace desired is set by the auto manufacturers. One way of expressing this shape mathematically, is to determine the torque: (a) when the flywheel speed is midway between the maximum constant speed selected and zero speed (such torque measurement is referred to herein as T.sub.D) and (b) when as the flywheel speed approaches zero rpm (such torque measurement is referred to herein as T.sub.O). Such torques can then be used to determine the torque ratio which is expressed as T.sub.O /T.sub.D, in which case the typical optimum value thereof is 1, or alternatively, to determine the torque differential T.sub.O -T.sub.D ; the typical optimum value of which is 0. (Thus, the optimum target value is achieved when T.sub.O =T.sub.D provided T.sub.D is within acceptable limits.) As the T.sub.O /T.sub.D increasingly exceeds 1, a transmission will typically exhibit shorter harsher shifts as it changes gears. On the other hand as T.sub.O /T.sub.D decreases below 1, there is an increasingly greater danger of clutch slippage when the transmission changes gears. Similar considerations apply with respect to T.sub.O -T.sub.D relative to the 0 target value.
Notwithstanding the above ideal target values, a T.sub.O /T.sub.D which exceeds 1, or a T.sub.O -T.sub.D which exceeds 0 is considered more undesirable than when T.sub.O /T.sub.D is less than 1 or T.sub.O -T.sub.D is less than 0. In short, harsh shifting is much more unacceptable than possible slippage.
While many automatic transmission fluids can achieve target values of T.sub.O /T.sub.D after a minimum number of cycles, it becomes increasingly more difficult to sustain such target values as the number of cycles are increased, e.g. to 18,000 as employed in the HEFCAD test. The ability of an ATF to sustain such desired friction properties is referred to herein as friction stability. Friction instability is a particularly significant problem when the ATF contains ZDDP. It is believed that as the ATF ages under the influence of the heat of friction, the ZDDP tends to break down and the decomposition products displace conventional friction modifiers at the metal/fluid lubrication boundary interface to an even greater extent than ZDDP itself. As a result, the fluid exhibits friction instability.
Attempts to solve the problem of friction instability by simply adding more friction modifier have not met with success because this tends to reduce the breakaway static torque (T.sub.S) of the fluid. This parameter when expressed as the breakaway static torque ratio (T.sub.S /T.sub.D) reflects the relative tendency of engaged parts, such as clutch packs, bands and drums, to slip. If this value is too low, the slippage can impair the driveability and safety of the vehicle.
Replacing ZDDP as an anti-wear additive to improve friction stability has also been difficult to achieve.
Very recently, more stringent requirements relating to automatic transmission fluids have been set by one or more auto manufacturers, e.g. as a result of fuel economy goals. The desire to enhance fuel economy has resulted in downsizing of cars and power trains, smaller engines and higher shift speeds, and increased usage of torque converter clutches, sprag clutches, and a shift to front wheel drive. The increased use of sprag clutches in automatic transmissions has caused a wear problem to surface which is extremely difficult to solve. Under high speed conditions, the inner race of the sprag clutch wears excessively. When this happens, there is a tendency for the sprags to flip and render the clutch inoperative.
Thus, transmission designs have undergone radical changes, thereby necessitating the formulation of ATF additives capable of meeting new and more stringent property requirements needed to match such design changes.
No base oil alone can even approach the many special properties required for ATF service. Consequently, it is necessary to employ several chemical additives, each of which is designed to impart or improve a specific property of the fluid. Consequently, it becomes particularly advantageous when one additive can perform more than one function, thereby reducing the number of additives needed to be present in the formulation.
Accordingly, there has been a continuing search for new additives possessed of one or more properties which render them suitable for use in ATF compositions, as well as other oleaginous compositions. The present invention was developed in response to this search.
U.S. Pat. No. 2,750,342 discloses hydrocarbylthio carbitol phosphates for use in improving the load carrying properties of a lubricating oil composition which phosphates exhibit a low pour point and high viscosity index. The carbitol portion of the phosphate is typically derived by reacting alkylene oxides with alcohols or mercaptans.
U.S. Pat. No. 3,828,084 discloses noncyclic thio phosphate esters for use as surface active agents. The thio phosphates are prepared by reacting an organic material with a phosphorous sulfide, e.g. P.sub.2 S.sub.5. The organic material may be any non-ionic surface active condensation product of from 1 to 150 moles of a C.sub.2 to C.sub.4 alkylene oxide with a suitable organic compound having about 5 to about 40 or more carbon atoms. Representative organic materials which are reacted with the phosphorous sulfide as disclosed at Column 7 include dodecyl mercaptan reacted with 6 moles of ethylene oxide. The resulting product can be characterized as an alkylthio carbitol phosphate. The thio phosphates disclosed in this patent may be used as petroleum additives. More specifically, they can be used as detergents or dispersants, in gasoline or in other fuels and they are useful in motor oils for detergency, sludge suspension, metal deactivation, etc.
U.S. Pat. No. 4,511,480 discloses phosphate esters of oxyalkylated thiols for use as corrosion inhibitors for ferrous metals in deep gas wells.
U.S. Pat. No. 4,263,150 discloses the use of metal salts, e.g. zinc salts, of phosphoro dithioic acids in combination with tri-organo phosphites to reduce the corrosive effect of the metal salt on copper. Suitable organic radicals of the tri-organo phosphites include substituted hydrocarbon radicals such as alkoxy, and alkyl sulfoxy.
U.S. Pat. No. 3,791,985 discloses sulfur containing phosphate esters of thio esters of phenols and alkoxylated phenols for use as additives to lubricants, such as mineral oils, especially cutting oils, and other working applications, gear lubricants, etc.
U.S. Pat. No. 2,280,450 describes hydrocarbon oils of improved resistance to corrosion containing a small amount of a substantially stable oil-soluble water-in-soluble reaction product of tricresyl phosphite and octyl phenoxyethanol. The mole ratio of tricresyl phosphite to octyl phenoxyethanol varies from 1:1 to about 1:2.5. The reaction product is described as a complex ester of phosphorous acid, which may or may not contain unreacted octyl phenoxyethanol.
U.S. Pat. No. 3,583,915 provides industrial fluid compositions and lubricant compositions containing improved load-carrying additives, including a diorgano hydrogen phosphonate in which at least one organic group in an aliphatic group containing at least 14 carbon atoms in admixture with an active sulfur compound.
U.S. Pat. No. 3,652,410 provides multifunctional lubricant additive compositions and lubricating oils containing, among other things, an organic acid phosphate or organic phosphite containing at least one alkyl or alkenyl group having from about 12 to about 24 carbon atoms. Also present is a mineral oil soluble or dispersible basic detergent, a mineral oil anti-oxidant, a sulfurized fat, or an alkyl sulfide or alkyl polysulfide.
U.S. Pat. Nos. 4,346,148 and 4,358,509 describe reaction products of alkoxylated alkyl phenol and a phosphorus trihalide which are included in lubricating compositions useful in metal-working operations, imparting corrosion resistance, extreme pressure properties, and protection against wear of working parts.
U.S. Pat. No. 3,115,465 provides antioxidant combinations for organic materials, including lubricants, comprising an oil-soluble alkyl, alkoxyalkyl, haloalkyl, cycloalkyl, halocycloalkyl, aralkyl, aryl, alkaryl, haloaryl or haloalkaryl phosphite ester; and from about 0.01 to about 5, preferably 0.25 to 2%, by weight, based on the oil, of a methylene bis-phenol.
Co-assigned U.S. patent application Ser. No. 612,666 filed May 21, 1984, discloses alkoxypolyethyleneoxy phosphite esters for use as water tolerance improving additives for lubricating oil compositions.
U.S. Pat. No. 3,524,909 discloses hydrocarbyl thioalkylene phosphites as thermal stabilizers for polyolefins. The alkylene group of the phosphite contains from 2 to about 20 carbon atoms and may be straight chain or branched. Additional inert substituents can be present, such as hydroxyl, nitro, alkoxy, halogen, and cycloaliphatic and aromatic groups. Thus, while the alkylene group may contain an alkoxy substituent, the alkylene group is not disclosed to contain repeating alkylene oxide groups. The nature of the polyolefins which are thermally stabilized by the subject phosphites is not disclosed in this patent.
U.S. Pat. No. 3,655,833 discloses hydroxybenzyl thioalkylene phosphites for use as a thermal stabilizer of organic polymer compounds against decomposition by heat, oxygen, and/or light. The alkylene group of the thio phosphite may also be replaced with a carboxy substituted alkylene group. Thus, the phosphites disclosed in this patent do not contain repeating alkylene oxide groups.
U.S. Pat. Nos. 3,045,042 and 3,117,091 both disclose partial esters of alkenyl succinic anhydride with a variety of polyhydric alcohols such as 2,2'-thiodiethanol as rust preventive additives in petroleum fractions such as gasoline and other fuels. U.S. Pat. Nos. 3,576,847 and 3,556,997 disclose sulfinyl-containing alkenyl succinates useful as dispersants, corrosion inhibitors and anti-wear agents in lubricating oil and fuel compositions, U.S. Pat. No. 3,381,022 generally discloses esters of C.sub.50 and higher hydrocarbon succinic acids suitable as additives in oils and fuels as well as being suitable plasticizers, detergents and emulsifiers.
U.S. patent application Ser. No. 359,801, filed Mar. 19, 1982, discloses and claims power transmitting fluid compositions containing the free esters of alkenyl succinic anhydride and polyhydric alcohols such as 2,2'-thiodiethanol.
U.S. patent application Ser. No. 763,254, filed Aug. 7, 1985, discloses certain metal salt (e.g. Ca), succinate esters and their use as friction modifiers.
U.S. Pat. No. 4,344,853 discloses zinc and nickel salts of the succinate esters, of thio-bisalkanols as anti-oxidants.
U.S. patent application Ser. No. 672,420, filed Nov. 16, 1984, discloses a two-component friction modifying combination of (a) the succinate ester of thio-bis-alkanols and succinic anhydride and (b) an alkyl or alkenyl diphosphite ester such as oleyl phosphite.